The recent study revealed that high-volume caudal block caused reduction in cerebral blood flow velocity and cerebral oxygenation. It was supposed to be associated with increased intracranial pressure. Ultrasonography of optic nerve sheath diameter shows a good level of diagnostic accuracy for detecting intracranial hypertension. The aim of this study is to evaluate the effect of caudal block on intracranial pressure in pediatric patients undergoing urologic surgery. Eighty patients, aged 6 months to 4 years, receiving caudal block before urologic surgery will be divided into high dose group (n=40) and low dose group (n=40). Randomly selected patients of the high dose group are given 1.5 ml/kg of 0.15% ropivacaine for caudal block. In contrast, patients in the low dose group are given 1.0 ml/kg of 0.15% ropivacaine for caudal block. The primary endpoint is the optic nerve sheath diameter after caudal block measured by optic nerve ultrasonography.